What does the PCV valve do?

I was just wondering what the PCV valve does and when and why it needs to be replaced? thanks

pcv stands for: Positive Crankcase Ventilation. it is an emissions control device that routes unburned crankcase gases back into the intake manifold where they can be reburned. besides eliminating crankcase emissions which cause air pollution, the constant recirculation of air through the crankcase helps remove moisture which causes sludge to form. thus the PCV valve extends the life of the oil and engine. from my experience, the pcv valve needs to be replaced because it get gummed up with oil and other sticky debris causing it to not open and close properly as a valve should, and will cause rough idle and/ or high pressure in the crankcase.

The PCV valve is basically a vacuum operated check valve for the crankcase. It's main purpose is to help pull oil vapor out of the crankcase and prevent crankcase pressure buildup. On 97-newer 3800 Grand Prix's, it is mounted under the MAP sensor in the intake plenum. If clogged or mis-installed, it can cause various trouble codes (mainly P0401) to pop up due to inaccurate vacuum readings at the MAP sensor. It should be changed on a regular basis like any filter, (GM recommended service interval is 12 mo, 12k miles, which is a little on the cautious side). I change mine every 25k or so. On other GM vehicles without this arrangement, the PCV isn't as critical, but if clogged will normally result in excessive oil consumption.

Just in case for any '97 - '03 L67 GTP owners referencing this your PCV valve is located on the back left hand side of the supercharger. It is not in the same location stated above for the normally aspirated Series II 3800.

Alright thanks. that sums it up well. Also I had a question about the cabin filter. Where is it located and does it just filter air going into the cabin like th a/c?

Alright thanks. that sums it up well. Also I had a question about the cabin filter. Where is it located and does it just filter air going into the cabin like th a/c?

For cabin air filter see link below:

http://www.mccgp.com/upgrades/cabinairfilter/air_filter.php

It is used when the AC is in the normal position not MAX. Also used in the vent mode. MAX pulls air in from the cabin and not outside via the cowl intake where the cabin air filter is mounted.